Cell therapy is emerging as an increasingly important technique for the treatment of diabetes and other conditions in which a reduction in pancreatic beta cell number or beta cell function is causative or contributory. In vitro, insulin producing (e.g., expressing) beta cells can be derived from various sources (e.g., human embryonic stem cells), but in general these cells are immature in their response to glucose, and although the cells contain and express insulin, they fail to secrete insulin in the presence of glucose or in response to changes in glucose concentration, as seen in recent publications (D'Amour et al., Nature Biotech., 24:1392-1401, 2006; Kroon et al., Nature Biotech., 26:443-452, 2008). Thus, renewable sources of beta cells that express insulin and secrete insulin in response to glucose are required for transplantation in cell therapy for diabetes.